1. Field of the Invention
The present invention relates to a foamed plastic comprising a copolymer of an N-alkyl-substituted maleimide and an olefin, and having high heat-resistance and high mechanical strength.
2. Description of the Related Art
Foamed plastics are used conventionally in a variety of application fields including trays, containers and the like in foodstuff packaging fields; heat-insulating materials, cushioning materials and the like in the fields of building-construction, industrial production, and commercial distribution.
The raw materials used usually for the foamed plastics include polystyrene, acrylic resins, polyvinyl chloride, and polyethylene. The foamed plastics made from the raw materials, however, are limited in the application field thereof because of insufficiency of heat-resistance, chemical resistance, mechanical strength, and so forth.
In the field of foodstuff, for example, the above-mentioned materials are not satisfactory for food containers for electronic range cooking in view of their insufficient heat-resistance. Further, the above-mentioned materials are not satisfactory for heat insulating material for automobile ceilings, roofs, steam piping, hot water piping, and so forth owing to the low heat resistance.
The inventors of the present invention made comprehensive study to solve the above problems, and have found that a foamed plastic constituted of a specified copolymer of an N-alkyl-substituted maleimide and an olefin is satisfactory for the above object.